Method and device for causing the eye to focus on a near object

ABSTRACT

An improved method and subconjunctival device for causing the eye to focus on a near object. The device automatically changes the focal length of the eye in response to a changing of the length of the medial rectus muscle or the inferior rectus muscle so that the eye can focus on a near object. The device is powered by a rechargeable battery and includes an electrode for stimulating the ciliary muscle as the length of the medial rectus muscle or the inferior rectus muscle changes.

RELATED PATENT APPLICATIONS

This patent application is a continuation in part of U.S. patentapplication Ser. No. 09/176,673, filed Oct. 21, 1998, now abandoned.

FIELD OF THE INVENTION

This invention relates to an improved method and apparatus for assistingan eye to focus on an object, and more particularly to an improvedmethod and an apparatus that is implanted in the body.

BACKGROUND OF THE INVENTION

It is well known that an aging lens precludes or diminishes a person'scapacity to focus on near objects. Focus is accomplished by changing thecurvature of the lens and the angular relation of the eyes to each otherin accordance with the distance of the observed object to the eye.

The change in curvature of the lens, called “Accommodation” iscontrolled by the circular fibers of the ciliary muscle which is anannulus that is connected to the lens by the zonules. When the ciliarymuscle is relaxed, the lens is flattened, i.e., it has less curvature.Thus, distant objects are in focus.

On the other hand, contraction of the ciliary muscle will cause thezonules to relax and the lens to thicken, i.e., it has more curvature,thereby shortening its focal distance to accommodate the viewing of anear object.

Accommodation causes the angular relation of the eyes to change such asby rotating them inwardly so that they turn toward the near object andso that they turn down. The inward rotation which is caused by themedial rectus muscles is called “Convergence.” The downward turningwhich is caused by the inferior rectus muscles does not have a specificname.

The amount of Convergence caused by an Accommodating lens is called theAccommodation—Convergence Ratio: $\frac{A\quad C}{A}$

where Accommodation is measured in diopters and Convergence is measuredin meter angles (m.a.).

The Accommodation—Convergence Ratio which is about 4:1 is constantthroughout life.

On the other hand, when the medial rectus muscle causes the eye to turntoward a near object, the lens accommodates a given amount. This is theConvergence—Accommodation Ratio:

C/A

The Convergence—Accommodation Ratio varies over a lifetime. For youngpeople, the ratio is about 4 m.a. per diopter. However, as a result ofageing the lens gradually becomes less elastic and the ciliary muscleweakens so that the ciliary muscle is not strong enough to cause thelens to adequately accommodate so that when the eyes converge 4 m.a.,the accommodation is less than one diopter and there is a failure tofocus. The reduction of the ability of the lens to accommodate is calledpresbyopia.

Therefore, as a person ages, more stimulation must be applied to theciliary muscle so that it can contract and maintain the 1:4 ratio.

As explained in Kamerling U.S. Pat. No. 4,603,697, which issued Aug. 5,1986, the content of which is hereby incorporated in its entirety byreference, the inability of the eye to focus on near objects can becompensated for by the use of an implanted electrode that can assist theeye to maintain focus. The electrode stimulates the ciliary muscle toconstrict and thereby thicken the lens to increase its curvature so thatit focuses on a near object thereby keeping the presbyopes in focus.

The system described in the Kamerling patent relies upon an external orinternal source of power which must be energized to stimulate theciliary muscle. That patent discloses that the stimulation can beachieved by using radio signals which are detected by an antenna.

It would be desirable if the lens could be automatically focused withoutexternal stimulation when a person changes the focus to read or see anear object.

SUMMARY OF THE INVENTION

Thus, with the foregoing in mind, the invention relates to a method forenabling the eye to focus on a near object comprising the step ofapplying an electrical stimulation to the ciliary muscle in response toa change in the length of the medial rectus muscle or the inferiorrectus muscle.

In another aspect the invention relates to a device for enabling the eyeto focus on an object. The device comprises an electrode forelectrically stimulating the ciliary muscle to change the focus of theeye. It also includes another implanted means for generating anelectrical signal in response to the movement of the medial rectusmuscle or the inferior rectus muscle, a battery, and electricalconnectors for connecting the battery, electrode and movement sensor.

DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic drawing of a device constructed in accordance withthe invention.

FIG. 2A is a front schematic view of the eye showing a sensorconstructed in accordance with the invention connected to the medialrectus muscle.

FIG. 2B is a front schematic view of the eye showing a sensorconstructed in accordance with the invention connected to the inferiorrectus muscle.

FIG. 3 is a graph showing the ratio of voltage signals necessary toaccomplish the result of the invention as a person ages.

FIG. 4 is a section of the eye showing the electrode inserted in theciliary muscle in accordance with the present invention.

FIG. 5 is a section of the eye showing the electrode inserted over thesclera adjacent the ciliary muscle in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a device 10 constructed in accordance with apresently preferred form of the invention is seen to include anelectrode 14 which is connected by thin wires 16 and 18 to an implantedrechargeable battery 24, a movement sensor 28 and a micro-chip 30.

As will be explained more completely, the rechargeable battery 24supplies a minute voltage signal to the electrode 14 by way of themicro-chip 30 when the movement sensor 28 detects a change in the lengthof the medial rectus muscle.

Referring to the FIGS. 2A and 2B, it can be seen that the motion sensor28 is connected to the medial rectus muscle 34 (FIG. 2A) or the inferiorrectus muscle 36 (FIG. 2B). The electrode 14 is inserted into theciliary muscle 40.

As is well understood, when a person tries to view a near object, themedial rectus muscle 34 and the inferior rectus muscle 36 of each eyeshortens slightly as the eyes turn in toward the object and down whilethe lens 48 thickens to increase its curvature and shorten its focallength.

In accordance with the invention and as seen in FIGS. 2A, 2B and 3, thechange in length of the medial rectus muscle 34 or inferior rectusmuscle 36 is detected by the sensor 28 which sends a first low voltagesignal A (FIG. 3) which is proportional to the change in medial rectus34 or inferior rectus 36 length to electrode 14 through the micro-chip30.

The micro-chip 30 includes a circuit (not shown) that emits a second lowvoltage signal B which is proportional to the first low voltage signalto stimulate ciliary muscle 40 and cause it to contract.

The contracted ciliary muscle 40 will consequently thicken the lens 48in proportion to the change in length of the medial rectus muscle 34.Therefore, the focal length of the lens 48 is shortened and the nearobject is brought into focus for viewing.

When the object is removed, the medial rectus muscle 34 and inferiorrectus muscle 36 relaxes, the first low voltage signal A is reduced, theciliary muscle 40 ceases to be stimulated and the lens 48 flattens topermit viewing of distant objects.

The ratio of the second low voltage signal emitted by the micro-chip Bfor a given first low voltage signal A is built into the micro-chip 30and is based on the amount of stimulation needed by the ciliary muscle.This can be determined individually for each person after examination.In the alternative it can be approximated by relying on the person's agesince rate at which Accommodation—Convergence Ratio deviates from the4:1 ratio as a person ages is known.

Further, as the person ages and the ciliary muscle 40 continue to weakenand the elasticity of the lens 48 continues to decrease, the amount ofstimulation that the ciliary muscle 40 will require to thicken the lens48 an amount sufficient to bring an object into focus will increase.Therefore, for given change in length of the medial rectus muscle 34 orinferior rectus muscle 36, and a corresponding first low voltage signalA that the change in length causes, the second low voltage signalemitted by the micro-chip 30 will have to be greater as that person agesto maintain the Accommodation—Convergence Ratio at 4:1 as seen in FIG. 3at B′ and B″.

The ratio of the second low voltage signal B, B′ or B″ to the first lowvoltage signal A necessary to accommodate the weakening of the ciliarymuscle and loss of elasticity of the lens can be increased by simplyreplacing the micro-chip 30 with one that has the preferred voltagesignal ratio built into it, or the micro-chip may be remotelyreprogrammed to provide the desired second low voltage signal B, B′ orB″ in response to a given first low voltage signal A.

In its presently preferred form, the device 10 is contained entirelywithin the body. The electrode 14 can be inserted into the ciliarymuscle as seen in FIG. 4 or the sclera adjacent the ciliary muscle asseen in FIG. 5. Hence, there are no antennae, electrodes, connecters orany other part extending through the skin.

The rechargeable battery 24 is recharged transcutaneously from time totime by magnetic induction in a manner similar to that describe in U.S.Pat. No. 5,411,537 or through a series resonant circuit such as thatdescribed in U.S. Pat. No. 5,279,292, or other similar suitableelectromagnetic recharging device 54. It will be apparent when therechargeable battery 24 requires recharging since this will be detectedby the diminution and ultimate inability of the eyes to focus on nearobjects.

The electrode 14 of the device 10 may be surgically inserted byperforming a limbal peritomy, pulling back a conjunctival tenons flap,grasping the wires 16 and 18 and the electrode 14 and inserting themthrough the sclera of the eye so that the electrode extends preferablyinto the circular fibers of the ciliary muscle 40 as seen in FIG. 4approximately 4 millimeters behind the limbus, and then closing theconjunctiva with sutures. While insertion into the circular fibers ofthe ciliary muscle is preferred, the electrode could be inserted intothe longitudinal fibers without impairing the operability of the device.

The rechargeable battery 24 and micro-chip 30 may be implantedsubconjunctivally in which case the wires 16 and 18 can runsubconjunctivally to the electrode 14.

Still further, the motion sensor 28 which may be comprised of a verythin wire can be sutured directly into or hooked onto the medial rectusmuscle 34 or inferior rectus muscle 36 so that its length changes inaccordance with the movement of that muscle, thereby varying the lowvoltage signal A applied to the micro-chip 30 and the low voltage signalB applied to the electrode 14.

The ratio of object distance to change of length of the medial rectusmuscle, i.e., Convergence, is incorporated into theAccommodation—Convergence Ratio and hence is well known by those skilledin the art. Similarly, ratio of object distance to change of length ofthe inferior rectus muscle, is well known by those skilled in the art.Accordingly, it is a relatively straightforward process to calibrate themicro-chip 30 so that constriction of the ciliary muscle 40 and theconsequent reduction in the focal length of the eye is proportional tothe change in length of the medial rectus muscle 34 or the inferiorrectus muscle 36.

When the device 10 is installed, the patient will be essentially unawareof its presence since it will operate to bring the lens 48 into focusautomatically in response to the movement of the medial rectus orinferior muscles 34 and 36 of each eye.

The only time that the device will require attention would be when therechargeable battery 24 requires recharging, which can be accomplishedby a suitable battery recharger 54, or when the micro-chip 30 isreplaced or reprogrammed.

While the invention has been described with respect to one presentlypreferred embodiment, it is apparent that other forms of embodimentswill be obvious to those skilled in the art in view of the foregoingdescription. Thus, the scope of the invention should not be limited bythat description, but, rather, only by the scope of the appended claims.

What is claimed is:
 1. A method of causing the eye to focus on a nearobject: comprising the step of applying an electrical stimulation to theciliary muscle in response to a change in the length of the inferiorrectus eye muscle.
 2. A method as defined in claim 1 wherein stimulationof the ciliary muscle causes the lens to thicken.
 3. A method as definedin claim 2 including the steps of providing: an implantable sensor forthe inferior rectus eye muscle, said sensor being operative to generatea signal in response to a change in the length of said eye muscle,implanting a means for stimulating the ciliary muscle, and said lastnamed means being operative to stimulate the ciliary muscle in responseto said signal from said sensor.
 4. A method as defined in claim 3including the steps of: implanting a rechargeable battery, said batterybeing operative to provide power for said sensor and for said means forstimulating the ciliary muscles.
 5. A method as defined in claim 4wherein said battery is recharged by electromagnetic energy.
 6. A methodas defined in claim 1 wherein said stimulation causes the ciliary muscleto contract in proportion to the shortening of the inferior rectus eyemuscle.
 7. A method as defined in claim 1 wherein said stimulationprevents or treats presbyopia.
 8. A method as defined in claim 4including the step of providing means for generating a signal tostimulate said ciliary muscle in response to said signal generated by achange in the length of said inferior rectus muscle, and implanting saidmeans for stimulating said ciliary muscle, said means for generating asignal, said battery, and said sensor being under the conjunctiva of theeye which is being focused.
 9. A device for enabling the eye to focus onan object, said device comprising: a first subconjunctivally implantablemeans for electrically stimulating the ciliary muscle to change thefocus of the eye said first implantable means controlled by a generatedelectrical, a second subconjunctivally implantable means for generatingsaid electrical signal in response to the movement of the inferiorrectus eye muscle, means for providing a source of electrical energy forsaid device, said last named means comprising a subconjunctivallyimplantable battery, and said means for generating a signal, said meansfor providing a source of electrical energy and said means forstimulating said ciliary muscles are adapted to be disposed under theconjunctiva of the eye which is being focused.
 10. A device as definedin claim 9 wherein said battery is a rechargeable battery, and means fortrans-conjunctivally recharging said rechargeable battery.